Today, environmental concerns and governmental regulatory schemes have challenged industry to reduce carbon dioxide emissions. For example, power plants are a major source of carbon dioxide emissions with worldwide emissions exceeding more than 2 billion tons of exhaust CO2 annually. Suitable CO2 capture processes require energy efficiency, and must exhibit targeted separation performance (e.g., high CO2 selectivity). Membranes have shown great promise in CO2 emissions capture, particularly in CO2 capture from power plant emissions, as a result of their operating simplicity and efficiency as compared to alternative separation technologies. Suitable separation membranes exhibit high permeance for undesirable species and the opposite for more valuable and/or favored species in order to concentrate the latter. For example, a practical membrane for CO2 capture from predominately H2, N2 and CH4 containing gases should exhibit a high permeance for CO2 as compared to CH4 and H2. In instances where permeation is adsorption-driven, the membrane necessarily exhibits high adsorption selectivity for the non-favored permeating species (e.g., CO2), and/or slow adsorption selectivity for the favored species (e.g., CH4 and H2).
The unique properties of metal-organic frameworks (MOFs) have demonstrated superiority over other gas separation and capture technologies due to their permanent porosity, ability to tune pore windows and cage-sizes, and chemical and thermal stability. MOFs are compounds including metal ions or clusters coordinated by organic ligands to form one-, two-, or three-dimensional porous structures. In the form of bulk solids and microcrystalline powder materials, MOFs have been used in many applications including sensing, gas storage and separation, catalysis, and drug delivery. However, the use of MOFs as membranes for gas purification and separation depends on the fabrication of continuous and defect-free MOF thin-films with good adhesion to supports, which has thus far proved challenging. MOFs can be produced by methods, such as hydrothermal or solvothermal techniques whereby crystals are slowly grown from a hot solution, but such methods are not suitable for MOF membrane fabrication.